BGM-71 TOW
The BGM-71 TOW series, also known as the Close Combat Missile System-Heavy, are second-generation SACLOS (semi-active command line of sight) guided anti-tank missiles, and the United States' principle ground-based heavy infantry antitank system. TOW stands for "Tube-launched, Optically tracked, Wire-guided" in most variants: in the case of RF-guided versions, the W instead stands for "Wireless." History TOW started development under the name heavy antitank weapon (HAW) and was developed in the 1960s as a replacement for the M40 recoilless rifle and the obsolete French-designed MCLOS anti-tank missiles in US service at the time (MGM-21A and MGM-32A ENTAC). The first concept mockup of the system was displayed at Redstone Arsenal in 1964. TOW saw its first use in combat in Vietnam in May 1972: this marked the first time that American soldiers had used an American-designed guided missile system in combat. TOW is the world's most heavily exported anti-tank missile system, with some 36 countries employing it by the 1980s, increasing to 43 as of 2018. Design Details TOW is an IR-based SACLOS system in which a thermal tracking system on the launcher tracks an active IR beacon on the missile's tail, generating flight corrections to guide the missile to the point of aim and transmitting them by command wires in most variants. The infantry TOW launcher consists of a series of modules which allow a team of soldiers to carry it broken down: the main assemblies are the sighting unit, launch tube, traversing unit, tripod, and the fire control subsystem (FCS) and silver-zinc battery power source (BPS). Older FCS modules have a space where a battery unit can be inserted into them if the BPS is not carried: the BPS grants a longer-lasting power supply and also includes a power conditioner to allow the missile to draw power from a vehicle's battery. The FCS connects to the launcher via a coil cable that is threaded through the bottom of the tripod: if a BPS is used, this connects to the FCS via its own cable. The missile in the TOW system is command-guided by the launcher: the missile's only function in the guidance system is to carry a thermal beacon on its tail so that the launcher's IR tracker can determine its location and compare this to the current position of the crosshairs. All flight calculations are handled by the FCS module, then handed off to the missile's control surface actuators via either command wires or a one-way RF datalink in wireless variants. While all TOW systems use IR tracking as part of their guidance, the M151 and M220 launchers do not allow the operator to see the output from the integral IR system: the basic daysight tracker is an optical system. To improve functionality at night or in severe weather, a gunner IR sight was developed that clips on top of the daysight tracker and has its own eyepiece. The first model was the AN/TAS-4 which was first issued with the M151 launcher: later, the improved AN/TAS-4A was developed. These are gas-cooled IR sights requiring the use of pressurised gas bottles to cool them to operating temperature. Firing procedure To load a TOW launcher, the shipping plug is removed from the missile tube's umbilical port, the front handling ring/cover is removed by releasing the metal band that secures it in place and pulling it off, and the tube inserted into the rear of the launcher's tube, locating it using the lugs at the front. The bridging clamp on the traversing unit is then closed and locked into place, establishing a connection between missile and launcher. The TOW missile uses an internal thermal battery to provide it with power during its flight time: due to this needing to warm up and the internal gyroscope having to spin up, there is a 1.5 second delay between pulling the trigger and the missile firing. During this time several distinctive sounds are heard: on pulling the trigger a "pop" is heard immediately, this sound being an explosive bolt detonating to open the compressed nitrogen bottle that spins up the gyroscope. After this a sound rather like ticking can be heard, this being the sound of the thermal battery heating up. TOW uses a soft-launch system with a small launch motor that burns for 0.05 seconds to eject the missile from the tube, burning out before it exits. The main engine only ignites when the missile's wings fully extend, this occurring about 7 meters (23 feet) from the launcher. The acceleration G-force from the flight motor firing is what arms the missile, typically about 0.53 seconds after launch when the missile is 65 meters (213 feet) from the launcher, making this the minimum effective range: this is intended to protect the operators in case of a launch motor failure. The flight motor burns out 1.6 seconds after launch, and the missile glides for the remainder of its flight time. The missile is first captured by the tracker about 1.85 seconds after launch: in wire-guided versions, if the tracker fails to detect the missile's thermal beacon at this point, the missile's command wires are automatically severed. The operator must hold the sight's crosshairs over the target until impact: a visible light beacon is provided to help track the missile using the daysight, while the IR beacon the launcher itself uses is visible when using the IR night sight. Maximum flight time is about 20 seconds. In wire-guided versions, the system will automatically cut the command wires just as the spools are emptied: in RF guided variants, the RF transmitter shuts down as the missile reaches its maximum range. Ammunition TOW missiles are issued packaged in a disposable protective launch tube with alignment lugs at the front end, an umbilical data connector on the top covered with a protective plastic cap in transit, and a moisture infiltration indicator in the middle of the rear bursting disc. Missile tubes have a 20-year shelf life and require no maintenance other than routine checks on their moisture indicators. Ammunition variants BGM-71A 1970: "Basic TOW," first production model, range of 3,000m. No longer produced. BGM-71B Also referred to as BGM-71A-1. Basic TOW variant with improved booster and extended control wires, giving a range of 3,750m. No longer produced. BGM-71C 1978: "ITOW," improved TOW with a collapsible standoff probe for better shaped-charge performance. No longer produced. BGM-71D 1983: "TOW-2," generally improved BGM-71C variant with guidance and flight motor improvements and an enlarged warhead. Changed tracking flare to emit pulses rather than a steady light to prevent the tracker being jammed by the Soviet Shtora active protection system. No longer produced BGM-71E 1987: "TOW-2A," tandem charge version optimized to defeat reactive armor, with a precusor warhead mounted on a long standoff probe on the missile's nose. Visual tracking beacon switched to a xenon lamp. BGM-71F 1987: "TOW-2B," overfly top-attack (OTA) variant using two downward-firing tantalum explosively formed penetrators, conceptually based on the 1985 Swedish RBS 56 BILL anti-tank missile. The two penetrators are fired at slightly offset angles to increase the probability of a hit. Uses a different flight profile to other TOW variants and a dual-mode laser/magnetic detonation sensor similar to the later FGM-172 SRAW to detect targets. The new warhead section was designed by Aerojet, with the triggering system by Thales Missile Electronics. Same improved Xenon beacon as 2A. TOW 2B Aero 2002: Sub-variant of the BGM-71F, using an aerodynamic nose cap that increase range to 4,500m (2.8 miles) and longer command wires. Gen2 version has enhancements to defeat active protection systems. BGM-71G F variant with a different top-attack warhead, never produced. BGM-71H "TOW-BB." BGM-71E modification with a bunker-busting warhead. TOW-RF Denotes a radio-frequency (RF) guided TOW. The RF system is contained inside the launch tube and requires no modification to the launcher, using the standard FCS and umbilical data connector. The missile itself is an E, F, 2B Aero or H variant. TOW-2N Original wireless TOW concept, cancelled in 1989. TOW-FF Fire-and-forget TOW with an imaging infrared focal plane array similar to the FGM-148 Javelin. Began work in 2000, cancelled by the US Army in 2002. BTM-71 Training version of the TOW, denotes a missile with a live booster but a dummy warhead. System variants M151 Basic TOW launcher. Original production only had a daysight tracker. M220 Improved TOW launcher designed alongside TOW-2 in the 1980s. Bradley TOW Twin-tube launcher developed for the M2 Bradley IFV. M65 Four-tube hardpoint-mounted launcher designed for helicopters. M41 ITAS Improved target acquisition system. 1999 redesign of the launcher with a combined sighting system, improved FCS, and improved lithium-ion power source (LPS). 709 systems were procured by the US Army from 1999-2003, and production restarted in April 2005. M41 ITAS-FTL ITAS-FTL adds integration with the Far Target Location system with a device called PADS (position attitude determination subsystem) that mounts on top of the ITAS scope. This gives precise GPS coordinate data and allows the ITAS system's laser rangefinder/designator to be used to target other weapons. IBAS Improved Bradley acquisition subsystem, equivalent of the ITAS upgrade for Bradley TOW launchers. Toophan Toophan (Persian توفان "Storm") is an Iranian clone of TOW, starting out as a straight copy mainly recognizable by the shorter legs of its tripod, before becoming a unique system with capabilities not present on the original TOW, in particular having missile variants with thermobaric warheads. Newer versions use semi-active laser homing (SALH) instead of IR. References Category:Anti-tank missiles Category:Missile launchers